1. Field of the Invention
The present invention relates to a method used in a time-division duplexing (TDD) system and related communication device, and more particularly, to a method of handling a measurement pattern for the TDD system and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Different from the LTE/LTE-A system operating in a frequency-division duplexing (FDD) mode (or simply FDD system), transmission directions of subframes of a frequency band in the LTE/LTE-A system operating in a time-division duplexing (TDD) mode (or simply TDD system) may be different. That is, the subframes in the same frequency band are divided into UL subframes, downlink (DL) subframes and special subframes according to the UL/DL configuration specified in the 3GPP standard.
FIG. 1 is a table 102 of the UL/DL configurations with subframes and corresponding directions. In FIG. 1, 7 UL/DL configurations are shown, wherein each of the UL/DL configurations indicates a set of transmission directions (hereinafter, directions, for short) for 10 subframes of a radio frame, respectively. Each subframe is indicated by a corresponding subframe number (i.e., subframe index) in FIG. 1. In detail, “U” represents that the subframe is a UL subframe where UL data is transmitted, and “D” represents that the subframe is a DL subframe where DL data is transmitted. “S” represents that the subframe is a special subframe where control information and maybe data (according to the special subframe configuration) is transmitted, and the special subframe can also be seen as the DL subframe in the prior art. Note that the eNB may configure a UL/DL configuration to a UE via a higher layer signaling (e.g., System Information Block Type 1 (SIB1)) or a physical layer signaling (e.g., DL control information (DCI)). In other words, the UE may receive the UL/DL configuration in the SIB1 from a broadcast control channel (BCCH), or in the DCI message from a physical DL control channel (PDCCH) or an enhanced PDCCH (EPDCCH). The UE performs transmission in a subframe in a radio frame if the subframe is a UL subframe indicated in the UL/DL configuration. The UE performs reception in a subframe in a radio frame if the subframe is a DL subframe or a special subframe indicated in the UL/DL configuration.
An information element MeasSubframePattern is defined in the 3GPP standard to specify a subframe pattern indicating subframes where the UE should perform measurements for channel quality reporting (CQI) reporting or Reference Signal Received Power (RSRP) reporting, or indicating subframes where an EPDCCH may be transmitted. The MeasSubframePattern can be set to one of subframeConfig1-5-r10 (corresponding to UL/DL configurations 1-5), subframeConfig0-r1 (corresponding to a UL/DL configuration 0) and subframeConfig6-r10 (corresponding to a UL/DL configuration 6). The subframeConfig1-5-r10 is a 20-bit bitmap, the subframeConfig0-r10 is a 70-bit bitmap, and subframeConfig6-r10 is a 60-bit bitmap.
An eNB may configure the subframeConfig0-r10 to a UE via transmitting a radio resource control (RRC) signaling (e.g., RRCConnectionReconfiguration), and the eNB may broadcast SystemInformationBlockType1 to indicate UL/DL configuration 0 to the UE. The UE performs transmission and reception in a radio frame according to the UL/DL configuration 0. In certain situations, the eNB may configure the UL/DL configuration 1 to the UE according to rapid changes of traffic loads on the UL and the DL (e.g., enhanced interference management & traffic adaptation (EIMTA)). The UE performs transmission and reception according to the UL/DL configuration 1 in a radio frame after receiving the UL/DL configuration 1. Accordingly, the UE does not know how to operate according to the MeasSubframePattern, if the MeasSubframePattern includes a subframeConfig corresponding to a UL/DL configuration (e.g., 0) which is different from the UL/DL configuration (e.g., 1) the UE is currently configured, e.g., by SIB1, a PDCCH or an EPDCCH.
In another example, the UL/DL configuration 1 is configured to a UE (e.g., via SIB1), and a subframeConfig1-5-r10 is configured to a UE by using a RRC signaling for an EPDCCH configuration. The subframeConfig1-5-r10 is a 20-bit bitmap which includes at least one bit set to “1”, and all the at least one bit corresponds to at least one DL subframe indicated in the UL/DL configuration 1. Therefore, the UE monitors the EPDCCH in subframes configured according to the subframeConfig1-5-r10. In certain situations, the eNB may configure the UL/DL configuration 4 to the UE by using a PDCCH or an EPDCCH due to rapid changes of traffic loads on the UL and the DL (e.g., EIMTA). Some UL subframes in the UL/DL configuration 1 are changed to DL subframes in UL/DL configuration 4. However, the eNB cannot transmit the EPDCCH to the UE via these DL subframes, because these DL subframes will not be used by the UE for the EPDCCH monitoring according to the subframeConfig1-5-r10. Therefore, flexibility of the scheduling is restricted.
Therefore, the inconsistency between the MeasSubframePattern and the UL/DL configuration configured to the UE is an important problem to be solved.